The invention relates to a packaging apparatus for closing a can with a closure member.
In general, cans as referred to herein differ from boxes or cartons in that cans are hermetically sealed, i.e., the contents are sealed in liquid-tight and preferably gas-tight fashion. Boxes or cartons, on the other hand, are typically closed simply by means of tabs or flaps or folded-in corner portions that do not provide for such tight, hermetic sealing.
A can is usually sealed with at least one closure member at a first end thereof. By connecting the can body to the closure member, the cylinder is given the desired shape cross-section, at least in the region of the closure element. After the can is filled, a further closure member may be sealed to the opposite end of the lateral surface or body member so that the can is completely sealed and the cylinder has a desired shape at the second end as well.
In case of a folded cylinder having at least two folding edges, the folding edges are formed (in particular bent and/or fluted) and circumferentially located in such a way that the lateral wall or body-forming portion of the can can be collapsed flat before insertion of a closure member. In the flat state, the volume of the cylindrical, body-forming member corresponds essentially to the material volume. In other words, essentially no empty volume is transported during transportation from the cylinder factory to the filling line. The foldable cylinder then is unfolded--preferably just before filling--and is sealed in the manner described above.
The closure members are initially completely separate from the lateral surface portion of the can body. They are, in general, formed as a single piece and comprise a closing surface, which is the same as the can cross-section, and an annular contact region by which they can be sealed tightly to the inside lateral can surface around the entire can circumference. (For purposes of the invention all continuous (i.e., unbroken), closed surfaces will be referred to as annular regardless of whether their contour is circular, oval, or polygonal and regardless of whether they are formed with straight or curved lines.)
Cans having a cardboard lateral surface are frequently cylindrical with the lateral surface being formed as a wound cardboard tube. In the case of a foldable cylinder having just two folding edges, the cross-section can become increasingly flat with increasing distance from a closure member, depending on the method of unfolding. Therefore, in order to achieve a better approximation to the desired circular cross-section along the length of the can, more folding edges can be provided, and a circular closure member be applied. In addition, the cylinder can be spread apart by a shaping means during unfolding, and/or the folding edges can be flattened out.
The final shape of the can also depends on the filling and on the second closure member. High resistance to deformation or crushing of the middle region of the can is achieved if the can cross-section is as circular as possible. However, elliptical closure members, those which comprise circular segments or parts of ellipses, or polygonal closure members (particularly having an even number of sides that are of the same length, and preferably having rounded corners) may also be provided instead of circular closure members.
With said can, it is also possible to provide unusual shapes in a simple manner. Specifically, the folding lines need not be flattened out, but can be used as the edges of a polygonal can cylinder. Accordingly, the closure members or the bottom and the lid would also be polygonal, i.e., the number of folding edges and the number of corners of the closure members would correspond. In particular, tetragonal, preferably hexagonal or even octagonal to dodecagonal cans can be provided with closure members according to the invention.
Since the "closed" (i.e., continuous) or annular contact surface of each of the closure members presses tightly against the inside of the lateral surface, the can or the foldable cylinder has excellent stability and seal tightness. Closure members having high tensile strength--e.g., closure membranes which are firmly connected to the inside of the lateral surface or body member in a tensioned state--may be used. The membrane comprises a plastic film or paper sheet, but preferably an aluminum foil, and is hermetically sealed to the internal lateral can surface.
If the closure member is firmly connected to a free cylinder edge along the edge, the cylinder is given the desired shape or cross-section at least in the region of the closure member. After filling, another closure member is mounted at a second, opposite region of the cylinder so that the can is closed and the cylinder is given the desired shape in the second end region as well.
For the insertion and sealing of closure members, preferably by means of a hot-melt adhesive, it is possible to use press apparatuses which press against the annular contact surfaces of the closure member and the cylinder from within and without (optionally from only one side) and supply heat to the contact surfaces during heat-sealing. Depending on the particular arrangement of the contact surfaces, the sealing surfaces lie either in the interior of the cylinder or along a separate sealing surface of the foldable cylinder.
A can closing press apparatus having at least one radially adjustable press surface is described in WO98/03278, for insertion of the closure member into a can. With such an apparatus, the press surface can be pressed against the contact surfaces after introduction of the apparatus. In the case of pressing from the inside of the cylinder, at least one press part (but preferably a plurality of press parts) having a convex press surface must be capable of being moved from a feed position in which it has a smaller press surface circumference to a pressing position in which it has a larger circumference. In the case of pressing from the outside of the cylinder, at least one press part (but preferably a plurality of press parts) having a concave press surface must be capable of being moved from a feed position in which it has a larger press surface circumference to a pressing position in which it has a smaller circumference. The parts which can be moved from the outside of the cylinder into their pressing positions may be dimensioned so that they form a step-free, closed (i.e., non-broken) circumferential line when they rest against one another.
However, such press apparatuses are mainly useful for cylindrically shaped can bodies having a circular cross-section. For non-circular shapes, such press appartuses become rather complicated, and if the cross-section becomes polygonal, a tight sealing in the corner edges is difficult to achieve.
U.S. Pat. No. 4,599,123 discloses a method for interconnecting a closure member with an annular contact region of the lateral can surface respectively jacket. The jacket is inserted in a weld ring with an entering cone edge. A press piston with a cone surface corresponding to the cone edge of the weld ring has to move down from a position distinctly above the weld ring. The press piston pushes the closure member into engagement with the jacket at the cone edge of the weld ring. The two cooperating press surfaces have conical sections in planes through the jacket axis, wherein the distance to the axis decreases towards the free end of the press piston. The weld ring supplies heat for welding the closure member to the jacket. After the welding the press piston has to move up and the jacket with the closure member can be pulled or pushed out of the weld ring. This solution has several disadvantages. The method is time consuming due to the movements of the press piston and the jacket. The press piston has to move quit a distance down and up. The jacket has to be inserted into and pulled out of the weld ring with the heat source. The welding is slow because only one press surface is at a high temperature. The cross section of the jacket is slightly increased at the free end of the jacket, due to the beveled press surfaces. This slightly outstanding jacket end is exposed to increased mechanical handling strain and causes problems with hooded lids.